In general, a high voltage semiconductor transistor device may one type of a power transistor, and may be used for a drive IC of a display device, servo motor, and/or an actuator requiring a high voltage operation.
Such a high voltage semiconductor transistor device may require a high breakdown voltage, and may use a lateral diffused MOS (LDMOS) or a lightly doped drain (LDD) structure.
FIG. 1 is an example cross-sectional diagram illustrating a related art semiconductor transistor device. The example semiconductor transistor of FIG. 1 is illustrated with an LDD structure.
Referring to FIG. 1, LDD region 12 may be formed at one side of P-type substrate 11, and may be made of silicon Si to a prescribed depth by a low concentration N− doping.
Further, drain and source regions 13 and 14 may be formed at LDD region 12 and another side of P-type substrate 11 to have a prescribed depth from a surface.
Gate poly layer 16 may be insulated from drain and source regions 13 and 14 through gate oxide layer 15.
Drain electrode D, source electrode S, and gate electrode G may be formed at drain region 13, source region 13, and gate poly layer 16, respectively.
As described above, in a related art design of a high voltage semiconductor transistor device, it may be important to obtain a high breakdown voltage.
To obtain a high breakdown voltage, an interval between an edge of gate poly layer 16 and drain region 13 may be adjusted. Namely, the high breakdown voltage may be obtained by adjusting a length expressed as “DR” in FIG. 1.
In FIG. 1, F may represent a generation position of a high voltage electric field, and an arrow may represent an electron flow path of a channel layer formed when applying a power source to gate electrode G.
To obtain the high breakdown voltage, “DR” may be increased. However, if “DR” is increased, a size of a transistor may also be increased.
Moreover, in a structure in which an electric current flows to a surface of LDD region 12, as the time of use of a device increases, a breakdown voltage may change.